Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.78   12.304%   $195.1619   $195.16   $195.15   $195.20  
  Purchase #2 $188.99   8.451%   $204.9615   $204.96   $204.95   $205.00  
  Purchase #3 $85.45   7.574%   $91.922   $91.92   $91.90   $91.90  
  Purchase #4 $201.32   6.204%   $213.8099   $213.81   $213.80   $213.80  
  Purchase #5 $126.48   13.615%   $143.7003   $143.70   $143.70   $143.70  
  Purchase #6 $46.69   11.135%   $51.8889   $51.89   $51.90   $51.90  
  Purchase #7 $99.81   6.612%   $106.4094   $106.41   $106.40   $106.40  
  7 purchase totals = $922.52       $1,007.8539   $1,007.85   $1,007.80   $1,007.90